Our friend is in a relationship with his dead brother’s daughter … it’s disgusting

DEAR ABBY: My husband’s best friend, “Kevin,” lost his wife three years ago. He’s currently in a relationship with his niece (his deceased brother’s daughter). Kevin is in his 60s; she’s in her 50s. We find this disgusting and do not condone it. They are both from Portugal. Is this acceptable in other countries?

We have tried to discuss it with him; he said he doesn’t care what we think. Kevin tries to plan things for all of us as couples, and we don’t want to be in their company. Am I wrong? I have known his niece for several years, and I don’t want to be unkind, but I just cannot be around them. His wonderful wife is turning over in her grave.

— SCANDALIZED IN NEW JERSEY